Microelectromechanical systems (“MEMS,” hereinafter “MEMS devices”) are used in a wide variety of applications. For example, MEMS devices currently are implemented as microphones to convert audible signals to electrical signals, as gyroscopes to detect pitch angles of airplanes, and as pressure sensors to detect changes in pressure. In simplified terms, such MEMS devices typically have a movable structure suspended from a substrate, and associated circuitry (either on or off chip) that both senses movement of the suspended structure and delivers the sensed movement data to one or more external devices (e.g., an external computer). The external device processes the sensed data to calculate the property being measured (e.g., pressure).
To form pressure sensors, many prior art processes form a cavity between a movable diaphragm and a base. To form the cavity, various processes known to the inventors remove an insulator material, which requires HF etches of a sacrificial oxide. Such etches, however, can create fabrication inefficiencies. Specifically, HF etches can harm metallization and pre-formed circuits, while causing stiction in compliant structures. In addition, such processes are relatively slow and thus, often have difficulty clearing out large cavities.